Conventional log turners known as “flying log turners”, typically comprise a pair of four to five foot long vertically oriented spiked rolls which are located on each side of a transporting conveyor. The log turner rotates a workpiece, such as a log, as the workpiece travels towards the infeed of a primary breakdown machine, such as canters, bandmills or circular Scragg saws. The spiked rolls of the log turner are movable laterally towards and away from the centreline of a workpiece, longitudinally along the length of the workpiece in an open-and-close operation, and vertically upwards and downwards to engage, manipulate, and rotate the workpiece. The pair of rolls moves in an open-and-close operation to control the location along the length of the log where the rolls contact and manipulate the log position. Each roll, or set of rolls also moves in the vertical direction.
Other conventional log turners known as knuckle turners provide a less accurate method of turning logs. If accurate turning feedback was achieved, this would be a more cost-effective method of turning the logs as compared to flying log turners.
As a workpiece travels along the conveyor en route to the primary breakdown machines, an optimizer, using data from a scanner, determines an optimized position of the workpiece such that the workpiece, when processed in accordance with the desired angular rotation of the optimized position, may generate the highest value or yield of lumber. To position the workpiece in the optimized position, motion control data generated by the optimizer and associated programmable logic controller (PLC) initiates movement of the log turner to rotate the workpiece in order to attain the optimized position. In flying log turners lateral and longitudinal displacement of the spiked turning rolls brings the rolls into contact with the surface of the workpiece. The vertical displacement of each spiked roll allows the workpiece to be rotated about its longitudinal axis. The log turner rotates the workpiece until the optimized position is achieved.
During the turning process, surface irregularities such as protruding knots or indentations on the surface of the workpiece may affect proper contact of the spiked rolls with the workpiece, thereby inhibiting proper rotation of the workpiece to position it in the optimized position. This turning inaccuracy results in a significant reduction in lumber recovery. Furthermore, even if the optimized position is achieved, movement of the transport conveyor on which the workpiece travels may not maintain the workpiece in the optimized position. Precision in workpiece rotation and workpiece positioning is made even more difficult given the high speed at which the log turner performs its function. By providing a system to improve the accuracy of workpiece positioning, lumber volume and value will thereby increase.
The scanner/optimizer decides what angular orientation the log needs to be in to get the highest value breakdown solution from the log. Motion control data is sent from the Optimizer to the PLC control system allowing the rolls to contact the log, and by moving the rolls in opposite vertical directions; the log can be rotated to the desired angular position.
During the log turning process, approximately eight feet along the length of the log is in contact with the turning rolls. Because the outer surface of the log typically exhibits many geometric defects such as knots, cat-face, etc., smooth & consistent contact with the turning rolls is impeded. This in turn results in the target angular position of the log not being reached. For example, as the rolls pass over a knot that is sticking out, optimal contact with the log is sacrificed and therefore the targeted position is not achieved. Depending on log geometry, log diameter and products being manufactured, this turning inaccuracy can have a significant impact on lumber recovery.